Ester production method by transesterification reaction using solid acid catalyst

ABSTRACT

It is an object of this invention to provide a method for producing an ester by a transesterification reaction in which the reaction can be stably performed in a short time at a pressure approximately equal to normal pressure. The ester is produced by a transesterification reaction in which a starting material ester and an alcohol are brought into contact with a solid acid catalyst that displays the characteristics of a very strong acid in terms of the absolute value of argon adsorption heat ranging from 15 to 22 kJ/mol. In particular, it is preferable that the starting material ester in a liquid phase and alcohol in a vapor phase be brought into contact with the solid acid catalyst, and that the starting material ester be oil or fat, and the alcohol be methanol or ethanol.

TECHNICAL FIELD

The present invention relates to a method for producing a fatty acidester or other ester by a transesterification reaction from atriglyceride, diglyceride, monoglyceride, or another starting materialester.

BACKGROUND ART

As disclosed, for example, in the following patent documents,transesterification reactions are used to produce fatty acid esters,with oils and fats, which are esters of fatty acids and glycerol,serving as starting materials. Caustic soda and other alkali catalysts,as well as zinc catalysts, lipases, and the like are used as thecatalysts. It has also been proposed to perform reactions in asupercritical state without adding a catalyst.

Patent document 1 Patent Publication No. 9-235573A

Patent document 2 Patent Publication No. 7-197047A

Patent document 3 Patent Publication No. 2000-143586A

DISCLOSURE OF THE INVENTION

The above reactions are time-consuming, and the process for separatingthe catalyst following the reaction is needed when caustic soda oranother alkali catalyst is used. In addition, when the starting materialcontains a large amount of free fatty acids, a pretreatment must beperformed in order to remove these acids. Alternatively, saponificationreactions may inhibit the transesterification reaction and bring aboutother drawbacks. The reaction must commonly be performed at a highpressure when a zinc catalyst is used or when the reaction is conductedin a supercritical state.

It is an object of the present invention to provide a method forproducing an ester by a transesterification reaction in which thereaction can be performed in a short time at a pressure approximatelyequal to normal pressure.

The inventors discovered that bringing the starting material ester andalcohol into contact with a solid acid catalyst that displays thecharacteristics of a very strong acid within a specific range couldstably advance a transesterification reaction. It is preferable in thiscase to bring a liquid-phase starting material ester and a vapor-phasealcohol into contact with the solid acid catalyst.

BEST MODE FOR CARRYING OUT THE INVENTION

Starting Material Ester

The starting material ester used in the present invention may be anyester containing an ester compound as its principal component, and maybe a polyester. In particular, a glyceride of a saturated or unsaturatedaliphatic carboxylic acid (carbon number of the carboxylic acid: about 8to 24) is preferably used. Specifically, triglycerides referred to asoils and fats are preferably used. Examples of such oils and fatsinclude soybean oil, coconut oil, olive oil, peanut oil, cottonseed oil,sesame oil, palm oil, castor oil, and other vegetable oils and fats, aswell as beef tallow, lard, horse fat, whale oil, sardine oil, mackereloil, and other animal oils and fats. The content of free fatty acids inthe starting material ester is 0 wt % to 30 wt %, and preferably 1 wt %to 20 wt %.

Alcohol

The alcohol used in the present invention is an alcohol with a carbonnumber of 1 to 3, and preferably methanol or ethanol, but a polyhydricalcohol may also be used. A mixture of these may also be used.

Solid Acid Catalyst

A solid acid catalyst which exhibits a very strong acidity in terms ofthe absolute value of argon adsorption heat ranging from 15 to 22kJ/mol, preferably 15 to 20 kJ/mol, is used in the present invention.When the acidity is expressed in terms of Hammett acidity function Ho,it is preferably within the range of −12 to −15. The argon adsorptionheat is the absolute value of adsorption heat obtained by heating themeasurement object to 300° C. while evacuating, introducing argon at thetemperature of liquid nitrogen, and measuring the amount of adsorptionby volumetry. The details are disclosed in J. Phys. Chem. B, Vol. 105,No. 40, p. 9667-(2001). The adsorption heat is commonly 50 kJ/mol orless.

It is preferable to use a solid acid catalyst in which a sulfuric groupor a Group VI metal component is supported on the surface of acrystalline metal oxide. The metal oxide may be an oxide of a singlemetal or a combination of metals selected from zirconium, hafnium,titanium, silicon, germanium, tin, and the like. Specific examples ofsuch catalysts include sulfated zirconia-based catalysts, sulfated tinoxide-based catalysts and other catalysts, which are described below.Group IV metal/Group VI metal-based catalysts (especially,tungsten/zirconia-based catalysts) are particularly preferable.

The specific surface area of the catalyst is preferably 50 to 500 m²/g,particularly 60 to 300 m²/g, and more particularly 70 to 200 m²/g. Thespecific surface area can be measured by the commonly known BET method.The pore structure of the catalyst can be measured by a nitrogenadsorption for pore diameters in the range of 0.002 to 0.05 μm, and by amercury porosimetry for pore diameters in the range of 0.05 to 10 μm.The pore volume with a pore diameter of 0.002 to 10 μm is preferably atleast 0.2 cm³/g, with a pore volume of 0.25 cm³/g to 1.0 cm³/g beingparticularly preferable. The central pore diameter of pore diameters inthe range of 0.002 to 0.05 μm is preferably 50 to 200 Å, andparticularly preferably 70 to 150 Å.

The catalyst preferably has a shaped form, or a so-called pellet shape,rather than a powdered shape, and one with a size of 0.5 to 20 mm can bereadily obtained. A catalyst whose mean grain size is 0.5 to 20 mm, andparticularly 0.6 to 5 mm, is preferably used. The mechanical strength ofthe catalyst, expressed as the side crushing strength of a cylindricalpellet with a diameter of 1.5 mm, is 1.0 kg or greater, and preferably2.0 kg or greater.

Sulfated Zirconia-Based Catalyst

In the sulfated zirconia-based catalyst, the metal component of at leastpart of the metal oxide comprises a zirconia (zirconium oxide) portion,which is a zirconium compound, and contains a sulfureous component.Generally, it is known that this type of catalyst has a Hammett acidityfunction Ho of −16.1. “Metal oxide” is defined as one comprising ahydrated metal oxide. The catalyst preferably comprises zirconia in anamount of 20 to 72 wt %, and particularly 30 to 60 wt %, in terms of theweight of the zirconium element. The proportion of the sulfureouscomponent is 0.7 to 7 wt %, preferably 1 to 6 wt %, and particularly 2to 5 wt %, in terms of the weight of the sulfur element. Catalyticactivity decreases if the proportion of the sulfureous component is toohigh or too low.

The zirconia portion preferably substantially comprises tetragonalzirconia. This can be confirmed by powder X-ray analysis or, in morespecific terms, by the diffraction peak of tetragonal ammonia at2θ=30.2° with the CuKα line. It is preferable that crystallizationproceed to an extent that can be confirmed by means of a diffractionpeak, and that no monoclinic zirconia be present. The ratio S28/S30 ispreferably 1.0 or less, and particularly 0.05 or less, where S30 is thearea of the diffraction peak of tetragonal zirconia with 2θ=30.2°, andS28 is the area of the diffraction peak of monoclinic zirconia with2θ=28.2°.

In addition, the catalyst preferably comprises aluminum oxide in anamount of 5 to 30 wt %, and particularly 8 to 25 wt %, in terms of theweight of the aluminum element. This alumina portion is preferablycrystallized, and, in particular, substantially consists of γ-alumina.

Sulfated Tin Oxide-Based Catalyst

The sulfated tin oxide-based catalyst comprises a tin oxide portion, inwhich tin is the metal component of at least part of the metal oxide,and also contains a sulfureous component. Generally, it is known thatthis type of catalyst has a Hammett acidity function Ho of −18.0. “Metaloxide” is defined as one comprising a hydrated metal oxide. The catalystpreferably comprises tin oxide in an amount of 20 to 72 wt %, andparticularly 30 to 72 wt %, in terms of the weight of the tin element.The proportion of the sulfureous component is 0.7 to 10 wt %, preferably1 to 9 wt %, and particularly 2 to 8 wt %, in terms of the weight of thesulfur element. Catalytic activity decreases if the proportion of thesulfureous component is too high or too low. The specific surface areaof the catalyst is preferably 100 m²/g or greater, and particularly 100to 200 m²/g.

As a characteristic of the tin oxide, amorphous tin oxide may also beused, but one consisting essentially of an oxide having a tetragonalcrystal structure is preferred. This can be confirmed by powder X-rayanalysis or, in more specific terms, by the diffraction peak at 20=26.6°with the CuKα line. Crystallization preferably proceeds to an extentthat can be confirmed by means of a diffraction peak, and thecrystallite diameter is preferably 10 to 50 nm, and more preferably 20to 45 nm.

The method for producing the sulfated tin oxide-based catalyst is notparticularly limited and, as an example, it is possible to use aproduction method in which a sulfur-containing compound is added to tinoxide, and the product is then calcined. The sulfated tin oxide-basedcatalyst may be in the form of a powder or a molded article, or in theform of a catalyst in which tin oxide is supported on the surface of asupport consisting of components other than tin oxide.

The tin oxide may be used in any form, and metastannic acid is usedparticularly preferably. The sulfur-containing compound is a compoundthat contains a sulfureous component, or a compound that contains asulfur component capable of being converted to a sulfureous component bysubsequent calcining or another treatment. Examples of suchsulfur-containing compounds include sulfuric acid, ammonium sulfate,sulfurous acid, ammonium sulfite, thionyl chloride, dimethylsulfuricacid, and the like. The sulfur-containing compound is commonly used as asolution such as an aqueous solution, and the solution is brought intocontact with the tin oxide.

Calcining is performed in air, nitrogen, or another gas atmosphere,although performing the process in air is particularly preferred. Thecalcining temperature varies with the calcining time, gas flow rate, andother calcining conditions, and is commonly 300 to 900° C., andpreferably 400 to 800° C. The calcining time varies with the calciningtemperature, gas flow rate, and other calcining conditions, and iscommonly 0.05 to 20 hours, particularly preferably 0.1 to 10 hours, andstill more preferably 0.2 to 5 hours.

Prior to contact with the sulfur-containing compound, the surface of thetin oxide is preferably pretreated with a solution, particularly anaqueous solution, comprising organic acid ions, particularly carboxylicacid ions. An aqueous solution of ammonium acetate or another ammoniumcarboxylate or carboxylic acid metal salt is preferably used as such anaqueous solution.

Group IV Metal/Group VI Metal-Based Catalyst

Group IV metal/Group VI metal-based Catalyst comprise, as their metalcomponents, one or more Group IV metal components selected from thegroup comprising titanium, zirconium, and hafnium, and one or more GroupVI metal components selected from the group comprising tungsten andmolybdenum. Especially, tungsten/zirconia-based catalysts comprisingzirconium as the Group IV metal component and tungsten as the Group VImetal component are preferred. Generally, it is known that this type ofcatalyst has a Hammett acidity function Ho of −14.6. The content of theGroup IV metal component in the catalyst is preferably 10 to 72 wt %,and particularly preferably 20 to 60 wt %, in terms of the weight of theGroup IV metal element. The content of the Group VI metal component inthe catalyst is preferably 2 to 30 wt %, particularly preferably 5 to 25wt %, and still more preferably 10 to 20 wt %, in terms of the weight ofthe Group VI metal element. The support is preferably substantiallycomposed of a metal oxide. “Metal oxide” is defined as one comprising ahydrated metal oxide.

In addition to oxides that may comprise hydrated oxides, the support mayalso comprise other metal components, for example, boron, magnesium,aluminum, silicon, phosphorus, calcium, vanadium, chromium, manganese,iron, cobalt, nickel, copper, zinc, gallium, germanium, yttrium,niobium, tin, lanthanum, cerium, and the like, either singly or incombinations thereof, as well as zeolites and other complex metaloxides. In particular, the catalyst preferably comprises aluminum in anamount of 3 to 30 wt %, and particularly preferably 5 to 25 wt %, interms of the weight of the aluminum element. Halogens may also becontained as needed in order to enhance the acid catalyst performance.The catalyst does not necessarily have to contain a sulfureouscomponent, but when a sulfureous component is contained, the proportionof the sulfureous component (SO₄) in the catalyst, expressed as theweight of the sulfur element, is commonly 0.1 wt % or less.

When the portion of Group IV metal component is made up of zirconia, thezirconia portion preferably substantially comprises tetragonal zirconia.This can be confirmed by powder X-ray analysis or, in more specificterms, by the diffraction peak of tetragonal zirconia at 2θ=30.2° withthe CuKα line. It is preferable that crystallization proceed to anextent that can be confirmed by means of a diffraction peak, and that nomonoclinic zirconia be contained. Specifically, the ratio S28/S30 ispreferably 1.0 or less, and particularly preferably 0.05 or less, whereS30 is the area of the diffraction peak of tetragonal zirconia with2θ=30.2°, and S28 is the area of the diffraction peak of monocliniczirconia with 2θ=28.20. If an alumina portion is present, the aluminapreferably is crystalline, and particularly preferably consistssubstantially of γ-alumina.

Method of Producing Group IV Metal/Group VI Metal-Based Catalyst

There are no particular limitations on the method of producing the solidacid catalyst, but to give an example, a producing method can be used inwhich the group VI metal compound(s) is/are added to a powder(hereinafter referred to as the ‘precursor powder’) of hydrated metaloxide(s) and/or metal hydroxide(s) that constitutes a precursor for themetal oxide(s) of the group IV metal component(s) constituting thesupport, and then kneading, shaping and calcining are carried out toproduce the catalyst. Hereinafter, description will be given for thismethod, but the order of shaping/calcining the support, mixing in thegroup VI metal component(s) and so on can be modified.

Precursor Powder of Group IV Metal Oxide

The precursor powder of oxide(s) of group IV metal(s) selected fromtitanium, zirconium and hafnium becomes the metal oxide(s) constitutingthe support through calcination after shaping; the precursor powder maybe produced in any way, but generally can be obtained by neutralizing orhydrolyzing metal salt(s), organometallic compound(s) or the like,washing and drying. Zirconium hydroxide (including the hydrated oxide)is preferably used as the group IV metal component precursor powder. Itis preferable to add a hydrated alumina such as boehmite to theprecursor powder. Furthermore, composite metal hydroxide(s) and/orcomposite metal hydrated oxide(s) can also be used in the precursorpowder. The amount added of the group IV metal oxide precursor powder ispreferably such that the content of the group IV metal component(s) inthe solid acid catalyst ultimately obtained is 10 to 72 wt. %,particularly preferably 20 to 60 wt. %, in terms of the weight of themetallic element(s).

Group VI Metal Compound(s)

Examples of the group VI metal compound(s) are oxides, chlorides,sulfates, nitrates and so on of tungsten or molybdenum, but aheteropolyacid of tungsten or molybdenum is preferably used, and atungstate or molybdate is most preferably used. The group VI metalcompound(s) may be used as is, or as a solution such as an aqueoussolution. The group VI metal compound(s) may be in a solid or liquidstate, and there are also no particular limitations on the concentrationof a solution, with it being possible to prepare the solution whileconsidering the amount of solution required for the kneading and so on.The amount added of the group VI metal compound(s) is preferably made tobe such that the content of the group VI metal component(s) in the solidacid catalyst ultimately obtained is 2 to 30 wt. %, preferably 5 to 25wt. %, particularly preferably 10 to 20 wt. %, in terms of the weight ofthe group VI metallic element(s).

Kneading

There are no particular limitations on the kneading method, with itbeing possible to use a kneader generally used in catalyst preparation.In general, it is preferable to use a method in which the raw materialsare put into the kneader, a solvent such as water is added, and kneadingis carried out using agitating blades, but there are no particularlimitations on the order of putting in the raw materials and additives.During the kneading, water is generally added as the above-mentionedsolvent, but an organic solvent such as ethanol, isopropanol, acetone,methyl ethyl ketone, or methyl isobutyl ketone may be added. Thetemperature during the kneading and the kneading time vary according tothe precursor powder of hydrated metal oxide(s) and/or metalhydroxide(s), which constitutes a raw material, and so on, but there areno particular limitations so long as these conditions are such that apreferable pore structure can be obtained. Similarly, acids such asnitric acid, bases such as ammonia, organic compounds, metal salts,ceramic fibers, surfactants, zeolites, clays, and so on may be addedwhen carrying out the kneading, so long as this is within a range suchthat the properties of the catalyst of the present invention aremaintained.

Shaping

There are no particular limitations on the method of shaping afterkneading, with it being possible to use a shaping method generally usedin catalyst preparation. In particular, it is preferable to useextrusion shaping using a screw extruder or the like, since shaping intoa desired shape such as pellets or a honeycomb can be carried outefficiently. There are no particular limitations on the size of theshaped article but, in general, the shaping is carried out to a sizesuch that the length of the cross section of the shaped article is 0.5to 20 mm. For example, in the case of cylindrical pellets, in general,ones having a diameter of 0.5 to 10 mm and a length of approximately 0.5to 15 mm can be obtained easily.

Calcining after Shaping

After the shaping, calcining is carried out in an atmosphere of a gassuch as air or nitrogen, although it is particularly preferable to carryout the calcining in air. The calcining temperature varies according tothe other calcining conditions such as the calcining time and the gascirculation rate, but is generally 400 to 900° C., preferably 500 to800° C. The calcining time varies according to the other calciningconditions such as the calcining temperature and the gas circulationrate, but is generally preferably 0.05 to 20 hours, particularlypreferably 0.1 to 10 hours, more preferably 0.2 to 5 hours.

Transesterification Reaction

The reaction temperature is such that the starting material ester is ina liquid state, and the alcohol is in a vapor state; specifically, thetemperature is preferably 100° C. or greater, and particularlypreferably 150 to 350° C. The reaction pressure is not particularlylimited and may be about 0.1 to 100 atm. Although the reaction will alsoprogress adequately at 0.5 to 2 atm, which is roughly equal toatmospheric pressure, it is preferred to conduct the reaction under 2 to100 atm, especially under 10 to 50 atm in which tungsten/zirconia-basedcatalysts are preferably employed. The reaction may also be conducted inthe so-called supercritical state. Nor is the reaction time limited, andthe product can be obtained in an adequate amount in about 0.1 to 1 hourin a batch reaction, and at a WHSV (weight hourly space velocity) ofabout 0.5 to 5 (/hour) in a flow reaction. The reaction may be a batchtype, flow type, or the like.

EXAMPLES

A more detailed description will be given below with the aid ofexamples.

Preparation of Sulfated Zirconia-Based Catalyst SZA

A powder that had a mean grain size of 1.5 μm and was obtained by dryingcommercially available dried zirconia hydroxide was used as the hydratedzirconia powder. Also, a commercially available pseudoboehmite powderwith a mean grain size of 10 μm was used as the hydrated alumina powder.1860 g of the hydrated zirconia powder and 1120 g of the hydratedalumina powder were blended, 575 g of ammonium sulfate was furtheradded, and the ingredients were kneaded for 45 minutes with a kneaderfitted with stirring blades while water was added. The resulting blendwas extruded from an extruder having a circular opening with a diameterof 1.6 mm, cylindrical pellets were molded, and the pellets were driedat 110° C., yielding dried pellets. Some of the dried pellets weresubsequently calcined at 675° C. for 1.5 hours, yielding a sulfatedzirconia-based catalyst (referred to hereinbelow as “SZA”). The zirconiaportion of the catalyst thus obtained consisted essentially oftetragonal zirconia.

SZA was used after cylindrical shapes with a mean diameter of 1.4 mm anda mean length of 4 mm obtained by calcining had been graded to a size of16 to 24 mesh. SZA had a specific surface area of 158 m²/g, and the porevolume of pores with diameters of 0.002 to 10 μm was 0.31 cm³/g. Thecentral pore diameter of SZA whose pore diameters were in the range0.002 to 0.05 μm was 5.5 nm. The argon adsorption heat was 24.3 kJ/mol.

Preparation of Sulfated Tin Oxide-Based Catalyst MO-817

100 g of commercially available metastannic acid (SnO₂, manufactured byYamanaka Industry) was dispersed in a 4-wt % aqueous solution ofammonium acetate, and the solution was filtered and dried for 24 hoursin air at 100° C., yielding precursor 1.4 g of the precursor 1 thusobtained was brought into contact with 60 mL of 6N sulfuric acid for 1hour, filtered, dried for 2 hours in air at 100° C., and calcined foranother 3 hours in air at 500° C., yielding a sulfated tin oxide-basedcatalyst (referred to hereinbelow as “MO-817”). The tin oxide portion ofthe catalyst thus obtained consisted essentially of tetragonal tinoxide.

MO-817 was in the form of a powder and had a specific surface area of152 m²/g, and the pore volume of pores with diameters of 0.002 to 10 μmwas 0.1 cm³/g. The central pore diameter of MO-817 whose pore diameterswere in the range 0.002 to 0.05 μm was 2.8 nm. The argon adsorption heatwas 31.0 kJ/mol.

Preparation of Tungsten/Zirconia-Based Catalyst MO-850

A powder that had a mean grain size of 1.5 μm and was obtained by dryingcommercially available dried zirconia hydroxide was used as the hydratedzirconia powder. Also, a commercially available pseudoboehmite powderwith a mean grain size of 10 μm was used as the hydrated alumina powder.1544 g of the hydrated zirconia powder and 912 g of the hydrated aluminapowder were blended, 808 g of ammonium metatungstate was further added,and the ingredients were kneaded for 25 minutes with a kneader fittedwith stirring blades while 1200 g of water was added. The resultingblend was extruded from an extruder having a circular opening with adiameter of 1.6 mm, cylindrical pellets were shaped, and the pelletswere dried at 110° C., yielding dried pellets. Some of the dried pelletswere subsequently calcined at 800° C. for 1 hour, yielding atungsten/zirconia-based catalyst (referred to hereinbelow as “MO-850”).The zirconia portion of the catalyst thus obtained consisted essentiallyof tetragonal zirconia.

MO-850 had a cylindrical shape with an average diameter of 1.4 mm and anaverage length of 4 mm, and had a mean crushing strength of 1.9 kg. Thespecific surface area was 101 m²/g, the pore volume of pores withdiameters of 0.002 to 10 μm was 0.32 cm³/g, and the central porediameter in the pore diameter range 0.002 to 0.05 μm was 105 Å. Theproportion of zirconia in MO-850, in terms of the weight of thezirconium element, was 38.0 wt %; the proportion of alumina, in terms ofthe weight of the aluminum element, was 13.0 wt %; the proportion of thetungstic acid component, in terms of the weight of the tungsten element,was 12.5 wt %; and the proportion of the sulfur component was 0.01 wt %or less. The argon adsorption heat was 17.6 kJ/mol.

Transesterification Reaction

These catalysts (4 cm³) were charged into a fixed-bed flow reactor witha length in the vertical direction of 50 cm and an inside diameter of 1cm and then soybean oil (manufactured by Kanto Kagaku) as a startingmaterial ester and methanol as alcohol were introduced from the topunder atmospheric pressure. The transesterification reaction was carriedout under the conditions shown in Tables 1 and 2, and the conversionrate of the soybean oil at the bottom outlet was measured by gaschromatography after 4 hours and 20 hours from the start of thereaction. The molar ratio of soybean oil and methanol was set to 1:40.The experimental results are shown in Tables 1 and 2. A catalyst-freeproduct obtained by charging the same volume of α-alumina powder insteadof the catalyst was measured for comparison purposes.

TABLE 1 Experimental Example 1 2 3 4 5 6 7 Catalyst SZA SZA SZA SZA MO-MO- MO- 817 817 817 Reaction 200 200 250 300 200 250 300 temperature (°C.) WHSV (/hour) 1.5 1.85 1.85 1.85 1.85 1.85 1.85 Flow rate of startingmaterial (g/hour) Soybean oil 3.3 3.0 3.0 3.0 3.0 3.0 3.0 Methanol 2.74.4 4.4 4.4 4.4 4.4 4.4 Conversion rate of soybean oil (%) After 4 45 37— 93 — — 69 hours After 20 41 27 56 78 10 18 67 hours

TABLE 2 Experimental Example 8 9 10 11 Catalyst MO- MO- MO- None 850 850850 Reaction temperature (° C.) 200 250 300 200 WHSV (/hour) 1.85 1.851.85 — Flow rate of starting material (g/hour) Soybean oil 3.0 3.0 3.03.0 Methanol 4.4 4.4 4.4 4.4 Conversion rate of soybean oil (%) After 4hours 48 86 — 0 After 20 hours 47 89 93 0

It was learned that although soybean oil was transesterified when a verystrong acid catalyst was used, SZA was susceptible to deteriorationduring the reaction, whereas MO-817 showed a low conversion rate,especially at the reaction temperature of 250° C. or less. The highestconversion rate was obtained when MO-850 was used and this catalyst wasnot subject to degradation during the reaction.

Further, a transesterification reaction was similarly carried out underthe reaction conditions shown in Table 3 in which the reaction pressurewas changed to 3.0 MPa.

TABLE 3 Experimental Example 12 13 14 Catalyst SZA MO-817 MO-850Reaction temperature (° C.) 250 250 250 Reaction pressure (MPa) 3.0 3.03.0 WHSV (/hour) 1.85 1.85 1.85 Flow rate of starting material (g/hour)Soybean oil 3.0 3.0 3.3 Methanol 4.4 4.4 4.4 Conversion rate of soybeanoil (%) After 20 hours 88.0 61.0 91.0

It is clear that the above catalysts all increased the conversion rateunder the pressurized condition. Especially, it is noted that the use ofMO-850 provided a further improved conversion rate in the reaction undersuch a pressurized condition, although it provided a fully enhancedconversion rate in the reaction under atmospheric pressure.

INDUSTRIAL APPLICABILITY

According to the present invention, a transesterification reaction canproceed in a short time under a pressure that is approximately equal tonormal pressure, and the product and catalyst can be easily separated.It is therefore possible to produce the desired ester with a highefficiency.

1. A method for producing an ester in which the ester is produced by atransesterification reaction comprising the step of bringing a startingmaterial ester and an alcohol into contact with a solid acid catalystthat displays the characteristics of a very strong acid in terms of theabsolute value of argon adsorption heat ranging from 15 to 22 kJ/mol,the solid acid catalyst comprising a Group IV metal component in acontent of 10 to 72 wt %, in terms of the weight of the Group IV metalelement, and a Group VI metal component in a content of 2 to 30 wt %, interms of the weight of the Group VI metal element.
 2. The method forproducing an ester according to claim 1, wherein the starting materialester is in a liquid phase and the alcohol is in a vapor phase.
 3. Themethod for producing an ester according to claim 1, wherein the startingmaterial ester is an oil or a fat, and the alcohol is methanol orethanol.
 4. The method for producing an ester according to claim 1,wherein the Group IV metal component is zirconium and the Group VI metalcomponent is at least one member selected from the group consisting oftungsten and molybdenum.
 5. The method for producing an ester accordingto claim 1, wherein the catalyst comprises aluminum in an amount of 3 to30 wt %, in terms of the weight of the aluminum element.
 6. The methodfor producing an ester according to claim 1, wherein the catalyst doesnot contain a sulfureous component.